There is a well-known difficulty in obtaining good adhesion between elastomeric coatings based on polar elastomers and non-polar rubber substrates. Useful elastomeric coatings have been made from such polar elastomers as carboxylated hydrogenated nitrile rubber (XHNBR) or ethylene acrylic terpolymers (AEM) in co-pending U.S. Pat. No. 6,884,412.
Common examples of nonpolar elastomers as substrates include as natural rubber (NR), polyisoprene (IR), polybutadiene (BR), styrene butadiene (SBR) and ethylene propylene (EPDM). One known method used to improve adhesion to a nonpolar elastomer substrate has been to treat the substrate with a chlorinating or oxidizing acid such as trichloroisocyanuric acid. This treatment is undesirable in many applications because the acid residue can cause corrosion to the spray equipment, dip tanks, and exhaust systems in the application lines and there is the suspicion that it may initiate corrosion of rubber to metal bonded parts that have been treated prior to coating.
Heretofore, commercial primers such as Chemlok® 254X have been used to enhance adhesion to EPDM, but is of limited use in preparing NR, BR SBR, and blends thereof for adhesion of polar overcoatings. Such nonpolar elastomers are most commonly used in dynamic applications ranging from tires to vibration isolators and dampers. Additional primers having ease of use and less corrosive are needed.
Conventional fluoroelastomers as coatings suffer from poor adhesion to many substrates and insufficient elongation when coated over flexible elastomers. Existing commercial fluoropolymer coatings delaminate and stress crack after limited flex-testing. Improved fluoroelastomer coatings are sought that provide curing in several hours and sufficient pot life to enable brushing, dipping and spray applications, and provide functional coatings on a variety of flexible elastomers, especially nonpolar elastomers.